P0401 EGR FLOW INSUFFICIENT

I'm working on my first EGR valve problem. I know they get dirty and can be cleaned, so I'm gonna give it a whirl.

I have a vacuum solenoid with markings of R, P, & Q, and another port with no marks that goes to the EGR itself.

The EGR (mounted on a 5S-FE, Toyota Camry) is difficult to access the mounting bolts, so I looked first at the vacuum solenoid. Sadly, I'm not sure what I'm looking at and could use some help.

I think I need a vacuum pump to proceed, but I'm not sure what I'm looking at.

Reply to
Jeff Strickland
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The device with P, Q, & R ports is not a vacuum solenoid, it is a vacuum modulator. To check the operation of the vacuum modulator:

1) disconnect the vacuum hoses from the modulator at ports P & R and from the EGR valve at Port Q. 2) Plug P&R 3) Blow into Port Q - you should be able to blow into port Q easily and air should flow through the filter. 4) Start the engine and rev to 2500 RPM 5) Repeat the test above - you should not be able to blow into port Q easily.

You can check EGR flow with the EGR valve still mounted on the vehicle by starting the engine and letting it idle, and applying vacuum directly to the EGR valve. When you apply vacuum directly to the EGR valve with the engine idling, the engine should start to stall. If the engine doesn't stall, the EGR valve isn't opening or it is clogged. If you don't have a vacuum pump, just find a vacuum hose with suction and plug it into the EGR valve.

You didn't mention mileage, model, or model year, which would be helpful, but I suspect that there is carbon built up inside the EGR tube. You might be able to get away with digging out the carbon, but the proper repair is to replace the EGR valve.

Reply to
Ray O

The car is an '01 Camry. I don't remember the miles, but 114k comes to mind.

I pulled the EGR off of the car and sucked on the vacuum port, and the diaphram pulls fully and smoothly. I did not investigate the tube that goes from the valve to the exhaust. The port on the EGR that bolts up to that tube is clear. There is a hose (rather large for a vacuum hose, but otherwise the same material) from the modulator thingy (I called this part a vacuum solenoid because that's what it is called when I found it in a parts catelog.) to the EGR. That hose is clear, and the port on the EGR is also clear. I'm don't know what that hose does, but the placement would make it a vacuum source when the EGR opens, and it should be a pressure when the EGR is closed since it is on the Exhaust Side of the EGR.

The modulator valve has a port that is not marked (where the relatively large rubber hose connects) on the bottom, and the P, R, & Q ports are on the top with small vac hoses connecting them to wherever they go. If I understand you correctly, the Q port should go to the EGR. Since I did not know the troublleshooting technique for the modulator, then I can't say which ports I blew into or what the results were. I did pull the part off of the car, so I did not test with the engine running.

I reset the Check Engine light, but it returned on the 2nd Drive Cycle -- which is expected because the monitor is for two cycles before the fault code is tripped. Actually, it wasn't expected at all, but since it is a two-cycle monitor, the light would not come on during the first cycle.

Reply to
Jeff Strickland

The vacuum solenoid is a rectangular box with 2 vacuum hoses and a wire attached. The vacuum solenoid electrically allows or blocks vacuum to the vacuum modulator.

If the EGR valve is still off of the car, look in the passage between the exhaust manifold & valve and between the valve & intake manifold to make sure they are clear.

If the EGR is back on, do the stall test. If the stall test passes, then the problem is with the vacuum circuit that controls the EGR valve. If the stall test fails, the problem is somewhere in the exhaust flow from the exhaust manifold to the valve to the intake manifold.

Reply to
Ray O

Okay, I'm looking at the modulator, and I have a vacuum pump.

Port Q does not go to the EGR. There is a port that goes there, but Q is not it.

I can draw air through Q, and hear airflow through P & R.

I connect the vac pump to the port that goes to the EGR, and I run the vacuum up to 20, and get the same result when I draw air through Q.

Port P I blow into P, and hear air coming out of Q. I can draw air from P, and there is resistance on Q

Port R I can blow and suck on R and hear air in Q

WITH THE VAC PUMP CONNECTED AND SET TO 20 Port P Same result. As I draw air, there is leakage at Q, but essentially the same result as without vacuum.

Port R Same as without vacuum.

Port Q Both with and without vacuum, I can hear air moving in both directions of P & R.

Does all of this mean the modulator valve is bad? This valve is easily replaced, and is cheap. Both good things!

Reply to
Jeff Strickland

Try this: Disconnect the vacuum hose from the EGR valve and plug the hose. Hook the vacuum pump to the vacuum port on the EGR valve itself, start the car, and let it idle. While it is idling, apply vacuum to the EGR valve.

If the engine still runs OK when you apply vacuum directly to the EGR valve, the EGR valve is bad or clogged.

If the engine starts to run rough or starts to stall, the EGR valve is good and take a closer look or swap the modulator.

Reply to
Ray O

If the car runs okay, then the tube to the exhaust manifold is clogged, is that right?

I already know the EGR diaphram works when vac is applied, but I did that test with the valve off of the car. I did this test, sorta, with the EGR off the car, and when vac is applied, the passage from the exhaust port to the intake port is opened. The ports themselves are clear, but I cannot see and did not fish a probe into the tube that goes to the exhaust manifold. The tube can be clogged, but there is no sign of such by an inspection of the ports themselves.

So, assuming the valve is good, if the car does NOT stall then there is no new intake source that should happen when the valve works because the tube that would create the intake source is clogged. Is that how it works? (I'm not fighting the test, I'm just trying to get my arms around why the results are what they are -- I want to understand, not merely do.) I think I asked the mechanical equivelent of a double negative, so please check for clarity...

If the engine runs, I have to remove the EGR again to clear the tube, and to recheck the operation of the diaphram. My untrained manner of cleaning the tube is to shove a coat hanger through it, or something. I can see how carbon can cake enought to not allow gasses to pass, but a coat hanger should be able to chip away at the carbon and clear the passage, shouldn't it?

Reply to
Jeff Strickland

The car started and ran okay until vac was applied, then it died. I put the modulator valve on and reset the codes. Waiting....

Reply to
Jeff Strickland

Bad news. The Check Engine Light just came back on. I guess the tube from the EGR back to the exhaust manifold must be clogged.

The valve works, the modulator is new, the vac lines are not dry or cracked. All that's left is carbon build-up in the tube. Crap! The EGR is difficult to remove.

Reply to
Jeff Strickland

When you connect the vacuum pump directly to the vacuum port on the EGR valve, let the engine idle, and then apply vacuum to see if the engine idles roughly or stalls, don't apply more than 14 in. Hg when you do the test because that is about what normal engine vacuum is. Pumping the vacuum higher than 14 In. Hg is not realistic engine operating conditions.

If you can install a vacuum gauge with a tee between the EGR modulator and EGR valve, there should be little or no vacuum at idle, then when you raise engine RPM to over 2,000 RPM, vacuum should rise as the EGR modulator supplies vacuum to the EGR.

Other possibilities that are causing the problem are a faulty EGR position sensor and a vacuum leak somewhere.

Reply to
Ray O

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